Magnetic induction intensity

Magnetic induction is a physical quantity used to describe the properties of a magnetic field. It is represented by B. The direction of the B at a point in the magnetic field is the direction of the magnetic field at that point, and the magnitude of the B indicates the strength of the magnetic field at that point.

In the SI system of units (international units), magnetic induction unit is volt seconds / m 2], and [] [] - volt seconds called Webb, so the magnetic induction unit is called 2] or [[Webb / M] [Special] Tesla, referred to as CGSM, in the system of units in the magnetic induction unit is [Gauss]. Units are represented by symbols: V is [volt], s is [sec], M is [M], Wb is [Weber], T is [Special], Gs is [Gauss], mT is [milli].

1T=1Wb/m2=104Gs=103mT (1)

2 、 continuity theorem of magnetic lines, magnetic flux and magnetic flux

We describe the magnetic field to the image with the flux, current generated by different magnetic field lines as shown in Figure 1, is around the current lines without clues of the closed line, current direction and magnetic direction to enter the right hand rule.

3, using Ampere's loop law

We can conveniently calculate the magnetic field produced by an electric current with some spatial symmetry. For example, calculation of magnetic field intensity of a uniformly dense ring around the internal solenoid P, as shown in figure 4. Take the point P, radius of concentric circular R, as a closed integral curve. Because of symmetry, the intensity of the magnetic field at each point on the concentric circumference is equal, and the direction of the magnetic field is in the tangential direction of the concentric circle, that is, alpha =0:

H * cos * dl=H*2 alpha Phi PI r=NI (11)

Then the magnetic field strength P: H=NI/ (2 - R)

Mode: N is the number of turns. It can be seen from this relation that the intensity of the magnetic field depends solely on the distribution of the current that produces the magnetic field, independent of the nature of the magnetic medium.

4 Law of electromagnetic induction

The law of electromagnetic induction shows the relation between the induction electromotive force and the flux change. The law states that the induced electromotive force in a loop is, for whatever reason, to change through the flux of a circuit:

E =-d phi /dt (12)

If the loop is composed of a N turn coil, then the induction electromotive force will be generated at each turn at the flux change, and the total induction electromotive force is equal to the sum of the induced electromotive force of each turn. When the flux of each pass is the same, there is:

E =N x D phi /dt (13)

The law of electromagnetic induction is one of the most commonly used laws in magnetic measurement.

When the magnetic flux in the formula (13) changes periodically according to the sine law, the relation between the effective value of the induced electromotive force and the maximum value of the magnetic flux can be deduced:

U = 4.44 x F X N * Phi m (14)

We specify that the tangential direction of any point in the magnetic field is the direction of the point magnetic field (that is, B), and the number of lines of force in the unit area perpendicular to the B vector is equal to the magnitude of the vector of the point B. That is to say, where the magnetic field is strong, the lines of force are denser and the magnetic field is weak, and the lines of force are scattered.

The number of total magnetic lines passing through a surface is called the flux through which it is represented by a phi. The calculation of magnetic flux, as shown in Figure 2, takes the area element on the surface, whose normal direction is a theta angle between the direction of the point and the B of the point, and the magnetic flux of the element through the area is:

D phi =B * cos theta * DS (2)

So the total flux of the S through the surface is

Phi Phi theta = B * cos * DS (3)

When the B is uniform and the S is flat and perpendicular to the B, the flux through the S plane is:

Phi =B * S (4)

This is often used in magnetic measurements.